The present invention relates generally to a sealing device, and more particularly, to a compound-type sealing device having a combination of seal lips, wherein a first seal lip is formed of a rubber-like elastic material and a second seal lip is formed of a resin material, and to a method of manufacturing such a compound-type sealing device.
It is well known in the art of sealing devices which have seal lips, to provide a sealing device which utilizes a seal lip formed of a rubber-like elastic material or a resin material such as PTFE (polytetrafluoroethylene). In a conventional sealing device where a seal lip formed only of a rubber-like elastic material is used, the seal lip may be damaged by contact with the fluid which is to be sealed, such as, oil or other chemicals. This may be very inconvenient. On the other hand, where a seal lip is used that is formed only of a resin material, the seal lip has the problem that the seal lip does not suitably follow-up the operation of a rotational shaft to be sealed due to a lack of elasticity of the resin of the seal lip and due to a leakage of fluid such as oil from a small gap.
The prior art has attempted to solve the aforementioned problems by providing a sealing device 100, as shown in FIG. 10, having only a resin seal lip 101, in which the elasticity of the resin seal lip 101 is improved.
In such a sealing device 100, the resin seal lip 101 has outer diameter side end portions 102 which are nip-supported by a pair of reinforcing rings 103 and 104. In order to improve the follow-up performance of the resin seal lip 101 to the rotation of the shaft and to prevent an oil leakage through the small gap, grooves 107 and 108 are formed so as to provide a bellows shape on the peripheral surfaces of the resin seal lip 101 on a side of the resin seal lip opposite the fluid to be sealed and on a side of the resin seal lip opposite a fluid side not to be sealed. These grooves 107 and 108 are formed by an upper die 111 and a lower die 112, as shown in FIG. 11, and are provided with mutually opposing projections 109 and 110 on the die""s pressing surfaces so as to provide grooves 107 and 108 on the upper and lower surfaces of the seal lip 101 as shown in FIG. 12.
Although the resin seal lip 101 of the conventional sealing device 100 has improved elasticity, the improvement in the elasticity is limited. The resin seal lip 101 still does not have as much elasticity as that of the seal lip formed of the rubber-like elastic material.
Furthermore, a sealing device 400, such as is shown in FIG. 13, is also well known. The conventional sealing device 400 includes a resin liner 407 which is bonded on a sliding surface 405 of a seal lip 402 formed of a rubber-like elastic material extending from a seal body 401 to the side of the seal lip opposite the fluid side to be sealed. The sealing device 400 thereby provides the elasticity of the rubber-like elastic material and improves durability of the sliding surface. The liner 407 has a sliding surface 403 on which is formed a helical groove 403 having a pumping function.
In such a conventional sealing device 400, however, the unsolved problem is that oil leaks through the small gap between the resin liner 407 and the rotation shaft 406.
In order to prevent the problems encountered in both the above-described conventional sealing devices, there have been further proposed various sealing devices of a compound type. Compound type sealing devices have a combination of a seal lip formed of a rubber-like material reinforcing ring 205 and the back-up ring 207.
FIG. 16 illustrates manufacturing processes of the aforementioned integral-compound type sealing device.
That is, a resin material 204A for forming a resin seal lip 204 is disposed in a mold cavity 507 of a rubber formation mold 506 constructed by upper first and second mold parts 501 and 502 and lower first, second and third mold parts 503, 504 and 505. The reinforcing ring 205 having the perforations 206 is disposed on the resin material 204A so as to abut against it, and under this state, a rubber material is vulcanized for forming the seal lip 203 of the rubber-like elastic material. Simultaneously with the formation of the rubber seal lip 203, the rubber material is baked integrally with a portion of the resin material 204A intruded into the cavity 507 and bonded thereto (refer to FIG. 16(a)).
Thereafter, as shown in FIG. 16(b), the upper first and second mold parts 501 and 502 are opened (in the direction of the arrow) to open the mold 506, and as shown in FIG. 16(c), the lower mold part 503 is pushed up in the direction of the arrow to form a lip front end portion. Then, as shown in FIG. 16(d), the lower second mold part 504, against which are resin material 204A abuts, is pushed up in the direction of the arrow, thereby separating the mold product from the mold 506.
However, even in the conventional compound type sealing device described above, a side of the lip facing radially inwardly, facing the shaft and the resin lip 204 of the seal lip 203 formed of the rubber-like elastic material is disposed adjacent to the resin seal lip 204, so that the resin seal lip 204 interferes with the rubber seal lip 203, thus providing the problem of poor follow-up performance with respect to the rotation shaft 202.
Furthermore, countermeasures for preventing the rubber material from rotating during manufacturing as well as the problems of dimensional performance in the formation of the resin seal lip 204 should be considered.
An object of the present invention is to solve the problems encountered in the prior art described above. A further object of the present invention is to provide a sealing device of a compound type having a combination of a seal lip formed of a rubber-like elastic material and a resin seal lip. A further object of the present invention is to provide a method of manufacturing the compound type sealing device capable of preventing the resin seal lip from interfering with the rubber seal lip. A further object of the present invention is to effectively prevent the rubber material from intruding during the manufacturing process. A further object of the present invention is to make the thickness of the resin seal lip relatively thin in order to improve the follow-up performance of the resin seal lip. A further object of the present invention is to reduce heat generation. A further object of the invention is to form the resin seal lip simultaneously with the rubber seal lip molding process.
The present invention provides a sealing device for sealing two members which are disposed to be relatively rotated mutually concentrically, the sealing device being provided with a first seal member having a seal lip formed of a rubber-like elastic material and a second seal member having a seal lip formed of a resin material to be assembled integrally with the first seal member, and characterized in that an annular space is formed between the rubber seal lip and the resin seal lip so as to prevent the resin seal lip from interfering with the rubber seal lip.
Accordingly, the resin seal lip becomes flexible following up the operation of a shaft without interfering with the rubber seal lip, thus improving the sealing performance.
It is characterized in that the annular space is formed between the resin seal lip and a side of the lip facing radially inward, facing the shaft and the resin seal lip of the rubber seal lip. This is because, in a conventional product, the side of the lip facing radially inward, facing the shaft and facing the resin seal lip of the rubber seal lip is most interfered with.
It is characterized in that an annular groove is formed to a side surface on the side of said annular space of the resin seal lip.
It is characterized in that a plurality of the annular grooves are formed in an axial direction.
The annular groove maybe formed continuous or partially discontinuous on an entire peripheral surface of the resin seal lip.
According to the formation of these annular grooves, the resin seal lip is liable to be flexed and hence the follow-up performance can be improved.
On the other hand, a helical groove is formed on a side surface opposite to the side of the annular gap of the resin seal lip to improve the sealing performance of the resin seal lip.
It is characterized in that the first seal member is provided with a reinforcing ring to which the rubber seal lip is integrally bonded.
It is characterized in that a film formed of a rubber-like elastic material is formed on the side surface of the gap side of the resin seal lip so that the rubber film is branched from a base portion of the rubber seal lip of the first seal member continuously therefrom.
Furthermore, a method of manufacturing a sealing device is characterized by the steps of:
preparing a mold for molding a rubber-like elastic material and a resin material having a flat washer shape;
inserting an outer diameter portion of the resin material into a mold cavity, and adhesively baking the rubber-like elastic material to the outer diameter portion of the resin material together with the molding of the rubber-like elastic material;
pressing an inner diameter portion of the flat washer shape resin material by a mold part adjacent to the mold cavity in utilization of a mold clamping pressure; and
bending the pressed inner diameter portion of the resin material under high temperature condition when a mold product is separated from the mold thereby to form a resin seal lip.
An annular projection is formed to an upper mold part to be pressed to form an annular groove to the upper surface of the resin material at a time when the inner diameter portion of the flat washer shape resin material is pressed to prevent the intrusion of the rubber material. Accordingly, it is not necessary to make thick the resin material as in the conventional technique to seal the surface contacting the mold and it becomes possible to reduce the thickness of the resin material to decrease tension force thereby to prevent heat generation from increasing.
Furthermore, it is characterized in that a helical projection is formed to a lower mold part to be pressed to form a helical groove to the lower surface of the resin material at a time when the inner diameter portion of the flat washer shape resin material is pressed.
It is characterized in that a part of the rubber-like elastic material is moved toward the upper surface side of the inner diameter portion of the resin material pressed from the inside of the mold cavity to form a rubber film thereon.
As described above, by moving a part of the rubber-like elastic material, the rubber-like elastic material easily flows in the mold cavity preventing formation of a defective product of the rubber-like elastic material.
In a case where a part of the rubber-like elastic material is intruded from the inner diameter side of the resin material to the lower surface side thereof through the inner diameter side end thereof, the intruded portion will be cut at the finishing process. However, the sealing device may be used with this intruded portion of the rubber-like elastic material if this portion does not affect on the sealing performance.